1. Field of the Invention
The present invention relates to the field of radios. More particularly, the present invention relates to a system providing a highly-linear, high-frequency power amplifier having low intermodulation products.
2. Description of the Related Art
Highly-linear, high-frequency power amplifiers that are used for multi-carrier code division multiple access (CDMA) and orthogonal frequency division multiplexing (OFDM) applications are a design challenge. Power amplifier nonlinearities generate intermodulation distortion products, and AM/AM and AM/PM distortions that result in co-channel interference and system self-jamming. Conventional techniques for overcoming amplifier nonlinearities include feedback and feed-forward techniques, predistortion and cascaded amplification. Feed-forward techniques have been used extensively, but provide inefficient performance and operation (less than 10% efficient). Additionally, feed-forward techniques require numerous circuit components and bulky delay lines that are inflexible once a design complete. Another approach is to connect multiple transistors in a parallel configuration at the output stage of a power amplifier so that each transistor operates with linear characteristics.
Nevertheless, what is needed is a linear RF power amplifier having a selectable output power level and a low intermodulation distortion level.